They are incredulous that the region could have accumulated that many mutations since the fusion. It is an argument from incredulity. Once this fallacy is thrown out many of the ICR arguments go away.
They will soon drop their arguments against this fusion and claim to understand the mutation as that Act-of-God that created the first man from the thin air and dust of the DNA chemistry.
They will see this evolution evidence as theistic in nature, because Gen 5:2 subtly announced that the first man and woman were called "Adams," as species:
Gen 5:2 Male and female created he THEM; and blessed THEM, and called
THEIR name Adam, (a species), in the day when THEY were created.
This is the transition of theology into the theistic use of Science in support of scripture.
In the short run, the aging elders of the churches will wiggle as much as they can around this fusion, which produces that much demanded Macro-evolution example they have used to resist the ToE.
The next generation will replace these elders with a story written in the stone of Science as Genesis, verse by verse, finds academic support,... forever.